Method using implantable wireless transponder using position coordinates for assessing functionality of a heart valve

ABSTRACT

A method for assessing functionality of a valve in a heart includes providing a position sensor that is a wireless transponder for transmitting or receiving an ultrasound wave for determination of position coordinates of the position sensor at the point; implanting the wireless transponder at a point on the valve; and using a position determining system for determining whether the valve is functioning properly based on position coordinates of the wireless transponder.

RELATED APPLICATIONS

This application is a Divisional application of U.S. patent applicationSer. No. 09/872,198 filed Jun. 1, 2001 now abandoned which is aContinuation application of U.S. patent application Ser. No. 09/381,753filed Apr. 13, 2000 now issued U.S. Pat. No. 6,498,944, which is aContinuation-in-Part Application of U.S. patent application Ser. No.08/595,365 filed Feb. 1, 1996, now issued U.S. Pat. No. 5,738,096 andPCT Application No. IL/98/00032 filed Jan. 22, 1998

FIELD OF THE INVENTION

The present invention relates generally to the field of intrabodyposition determination, and specifically to intrabody measurements usingposition determination.

BACKGROUND OF THE INVENTION

There are many cases in which it is desired to measure organs or spaceswithin a patient's body. One such case is in preparation for organtransplantation. In transplantation procedures, in order to speed up thetransplantation procedure and minimize the period in which the patientis without the transplanted organ, the new organ is preferably preparedbefore the transplantation procedure. In order to ensure properreception of the new organ, it must be as similar as possible to theorgan that is removed. In some organs the similarity in size may beapproximate, since the surroundings of the organ are elastic. However,in other cases, the new organ must fit precisely in place of the oldone.

In other cases, an empty space within a body is to be filled. Forexample, a patient may be missing a piece of a bone which is to bereplaced by an artificial implant. Precise measurement of the spaceallows preparation of the artificial piece before its implantation, andmay enable automatic fabrication of the artificial piece.

Measurements within a patient's body may be used also for other reasons,such as inspection and diagnosis. For example, in some cases, a tumormay be analyzed according to its size and/or its shape to track theprogress of therapy or to plan a surgical operation. In tumor removalsurgery, measurement of the tumor before, during, and after the surgerymay be performed to verify removal of all or a desired portion of thetumor.

In the art, measuring an organ or a space within a body is usuallyperformed on CT or MRI images, or using ultrasound. U.S. Pat. No.5,370,692 to Fink et al., which is incorporated herein by reference,describes a method of approximately fabricating prosthetic bone implantsaccording to a CT image. However, these measurements are less accuratethan direct measurements of the bone dimensions. In addition, someorgans have a complicated geometry and therefore are hard to measureeven on accurate images. Furthermore, some organs, such as the heart,are in movement and cannot be imaged fast enough to allow production ofa clear and still image which can be measured.

There has been a system proposed for producing a prosthetic device,based on an arm which is connected through motion detectors to a modelcarver. A tip of the arm is moved on an outer surface of an organ, so asto produce a model of the organ. The use of such arms is limited toorgans which are easily accessible to the arm, and therefore in mostcases this system cannot be used in minimally invasive procedures. Inaddition, using more than one arm simultaneously is very difficult,since multiple arms interfere with each other.

When aligning bones, regions between bone fractures should be of minimalsize, to ensure that the bone properly heals. Ordinarily, one or moreX-ray images are taken of the broken bone, and the pieces are alignedaccordingly. However, when the fracture is complicated, many images maybe necessary, causing the surgeon and patient to be exposed to largeamounts of radiation.

U.S. Pat. No. 5,558,091 describes a method of aligning sections of abroken bone, by observing a continually-updated image. The image isinitially acquired using X-rays, but is then updated by computer imageprocessing, based on a position determining system which tracks themovements of sensors attached to the bones. However, this methodrequires producing a separate sub-image for each bone section, andtherefore is not suitable for multiple fracture pieces. Also, it wouldbe useful to have a method of accurately realizing the proper alignmentof the bones independent of the images.

SUMMARY OF THE INVENTION

It is an object of some aspects of the present invention to provide amethod for accurate measurement of organs and spaces within a humanbody.

It is another object of some aspects of the present invention to providea method of three-dimensional mapping of an organ situated within ahuman body.

It is a further object of some aspects of the present invention toprovide a method for producing a three dimensional model of an organwhich is situated within a human body.

Another object of some aspects of the present invention is to provide amethod of aligning bone fractures without unduly exposing the patientand staff to large amounts of radiation.

Another object of some aspects of the present invention is tocontinuously report volumes or other sizes of regions between intrabodyorgans, such as bone fractures.

In some preferred embodiments of the present invention, one or moreminiature position measuring sensors are placed at selected pointswithin a patient's body. A position determining system, preferablysituated outside the patient's body, determines the coordinates of thesensors. Calculating circuitry associated with the position determiningsystem calculates distances between the points, based on thecoordinates. Thus, an organ can be measured by placing the sensors atextreme points of the organ and determining the coordinates of thepoints.

Preferably, the position determining system determines positions basedon transmitting and detecting electromagnetic waves, and the sensorscomprise miniature coils, in which currents flow responsive to theelectromagnetic waves. Alternatively, the position determining systemmay operate using infrared or ultrasound waves or any other suitablenon-ionizing fields, and the sensors accordingly comprise suitabletransponders.

In some preferred embodiments of the present invention, position sensorsare mounted onto or embedded within an object, for example, a screw,staple, electrode or shunt, which is implanted in the body. The positionsensors may be used both for guiding the object into the body, and lateron for measurement of intrabody spaces that the object adjoins.

In some preferred embodiments of the present invention, the sensors areplaced at a plurality of points on an outer or inner surface of anorgan, while the position determining system continuously determines andrecords the coordinates of these points, preferably at a high samplingrate. The calculating circuitry calculates the size of the organaccording to the recorded coordinates. Preferably, the sensors aremounted on the tip of one or more catheters, so as to allow easymovement of the sensors along the surface of the measured organ.

In some preferred embodiments of the present invention, one or morereference sensors are placed within the patient's body for use in makingan intrabody measurement. These reference sensors are fixed in place byan operator of the catheter, for example, by a surgeon and aresubstantially not moved thereafter, during the measurement. Thereference sensors are preferably fixed to one of the patient's organs,such as the heart, so that the movements of the reference sensors followthe movements of the patient or of the organ. The coordinates of thereference sensors are determined by the position determining system andare used by the calculating circuitry to transform the (time-varying)coordinates of the recorded points to a stationary coordinate system.Preferably, for each point that is recorded, the position determiningsystem determines simultaneously the coordinates of the measuringposition sensor and of at least one of the reference sensors. Thecalculating circuitry transforms the coordinates of the point to a frameof reference that is fixed to the moving organ.

Preferably, measurement of the organ is performed using a catheter,which may be inserted into the patient for other purposes, as well. In apreferred embodiment of the present invention, a heart valve is examinedusing a measuring catheter, before and after a valve replacementprocedure. Preferably, the valve is replaced in a minimally-invasiveprocedure, using, for example, the Port-Access (™) MVR system, suppliedby Heartport Inc. The position information determined during theexamination before the replacement procedure is used to provide anaccurate measurement of the valve for the purpose of preparing asuitable prosthesis.

In order to perform the measurement, a catheter with one or moreposition sensors mounted on its tip is inserted into the patient's heartand brought into proximity with the valve. The catheter preferably alsoincludes a flow or pressure sensor, which is used for determining ratesof blood flow through and in the vicinity of the valve, at a pluralityof time points. The surgeon may determine accordingly the blood flowpattern in the vicinity of the valve. Preferably, the surgeon alsocorrelates the flow information with the valve state, i.e., when thevalve is open and when it is closed. The valve state is determined, forexample, by fixing a position sensor to the valve and allowing thesensor to drift freely with the valve, while the position determiningsystem determines the sensor's position. Preferably, the position sensoris detachable from the catheter, so that the catheter may place thesensor and then move on to other positions in which the flow or pressureis to be measured, simultaneously with determining the state of thevalve. The detachable sensor may either be connected through signalwires to the catheter or be a wireless position sensor. The surgeon usesthe information thus gathered in deciding whether to replace the valve.

If the valve is to be replaced, it is immediately measured, preferablyusing the catheter already in the heart, so that a replacement valve ofthe same size can be prepared. During measurement, the tip of thecatheter is systematically brought into contact with a plurality ofpoints on the circumference of the valve, in order to determine aplurality of points forming a map of the valve. The number of points tobe determined depends on the desired accuracy of the valve sizemeasurement.

In order to compensate for changes in position of the measuring catheterdue to the movements of the heart, a reference catheter, with one ormore reference position sensors, is preferably placed at a fixed pointon or, preferably, within the heart. For each point touched by themeasuring catheter's tip, the position determining system records theposition of the tip, and simultaneously, the position of the referencecatheter. The calculating circuitry receives the positions of thedetermined points and compares the position of the measuring catheterrelative to the reference catheter, so as to map the points contacted bythe measurement catheter in a frame of reference fixed to the heart.According to these calculations a map of the valve is produced.

Preferably, a parameter characteristic of the tissue adjacent eachrecorded point is also determined, so as to ascertain whether the pointis actually on the valve. This parameter may be, for example, the localelectric activity, since the electrical activity of heart muscle tissueis substantially greater than that in the valve.

The accuracy of the map depends on the number of points on the valvewhich are recorded. If not enough points were recorded in order toproduce a map of satisfactory point density, the calculating circuitrypreferably prompts the operator to measure additional points. After thecircumference of the valve is properly mapped, the calculating circuitrypreferably reports the size and volume of the valve.

According to the map and reported size, a new valve, preferably aflexible valve which is inserted using a minimally invasive method, isprepared for implantation. Preferably a catheter with a position sensoris also used during the implantation procedure, to locate points whichwere mapped earlier. The surgeon can use these points as a reference, toassist him in accurately inserting the new valve into its place. Afterthe implantation, the catheter is preferably used again to check whetherthe new valve operates properly, in a manner similar to the diagnostictests performed before the implantation.

In other preferred embodiments of the present invention, positionsensors are used in measuring and aligning bone fractures, generally inorder to minimize the distance and/or space between pieces of fracturedbone that are being fixed. Position sensors are fixed to each of thepieces of the fractured bone, using screws, adhesive or any othersuitable connection method.

In order to calibrate the sensors before beginning the fixation, theregion of a fracture is imaged using any suitable imaging method knownin the art, such as fluoroscopy or MRI. Simultaneously, positioncoordinates of the sensors are determined and recorded using theposition determining system. An image, preferably a three dimensionalimage, of the fracture pieces is displayed on a screen. The positioncoordinates of the sensors are registered with specific points in acoordinate frame associated with the image, and the contours of eachpiece are linked with the respective sensor. Preferably, each point inthe image which represents part of a fracture piece is linked with oneof the sensors. When the fracture pieces are moved, the display on thescreen is updated according to the position coordinates of the sensors,which are updated continuously by the position determining system. Thusan on-line image of the bone fracture is produced, enabling easyalignment of the fracture, without requiring additional imaging.

In one of these preferred embodiments, during calibration, which ispreferably performed after the patient's skin covering the bone issurgically opened, an external probe with a position sensor at its tipis passed over the surface of the fracture pieces. The positiondetermining system determines and records the positions of a pluralityof points on the surface of each piece, using the sensor within the tipof the external probe. The points on the surface of each piece arepreferably registered relative to the sensor connected to the piece, soas to compensate for movements of the piece during calibration. Thus,for each fracture piece, the calculating circuitry records thecoordinates of the sensor connected to the piece and coordinates of theplurality of points received during calibration, so that the positionand shape of the entire piece can be determined based on the positionand orientation of the position sensor fixed thereto. During alignmentof the bone, the image of the bone is thus precisely updated.

In some of these preferred embodiments, the circuitry produces andupdates an estimate of the distance and/or volume between the fracturepieces, based on the position coordinates of the sensors. To calculatethe distance from a piece to its neighboring pieces, the calculatingcircuitry preferably finds for each of the plurality of points on thepiece the closest determined point which is not on the same piece. Thedistance to this closest point is used to estimate the distance andvolume between the pieces.

When the volume is smaller than a predefined value, the calculatingcircuitry preferably signals the surgeon that the pieces are properlyaligned. Alternatively, when the volume cannot be reduced to within thepredefined value, the calculating circuitry may be used to report thedimensions of the region, so that a prosthetic implant can be fabricatedaccordingly. After the bone is properly aligned, the sensors may beremoved from the bone.

In a further preferred embodiment of the present invention, thecalculating circuitry is coupled to modeling apparatus whichautomatically fabricates the prosthetic bone implant.

In another preferred embodiment of the present invention, sensors areconnected to vertebrae of the spine during back surgery. The distancesbetween the sensors are constantly reported to the surgeon, whoaccordingly aligns the vertebrae.

There is therefore provided in accordance with a preferred embodiment ofthe present invention, a method of measuring the size of an area withina body, comprising bringing at least one position sensor to each of aplurality of points in the area, determining position coordinates of theplurality of points, using the sensor, and calculating distances betweenthe plurality of points.

Preferably, bringing the at least one sensor to the plurality of pointscomprises bringing the distal end of a probe with the at least onesensor mounted thereon into contact with each of the plurality ofpoints.

Preferably, bringing the distal end into contact with each of theplurality of points comprises passing the distal end over a surfaceadjacent the area.

Preferably, bringing the at least one sensor to each of the plurality ofpoints comprises bringing the at least one sensor to a plurality ofpoints within an organ.

Alternatively or additionally, bringing the at least one sensor to theplurality of points comprises bringing the at least one sensor to aplurality of points on the circumference of an organ.

Alternatively or additionally, bringing the at least one sensor to theplurality of points comprises bringing the at least one sensor to aplurality of points on one or more pieces of a fractured bone.

Preferably, determining the positions of the points comprisestransmitting and receiving magnetic fields.

Preferably, the method includes constructing a geometrical map of theplurality of points.

Preferably, the method further includes displaying the map inconjunction with a three dimensional image of a corresponding portion ofthe body.

Preferably, the method includes calculating a volume associated with thearea.

Preferably, the method includes producing a model of the area based onthe distances.

Preferably, the method includes identifying a region of the area inwhich there is less than a predetermined density of determined points,and prompting a user to bring a sensor to the region to determinecoordinates of additional points.

In some preferred embodiments of the present invention, the area is inmotion, and the method includes associating at least one referencesensor with the area, so that the reference sensor moves with the areadetermining the position of the reference sensor when the position of apoint is determined, and comparing the positions of the plurality ofpoints to the position of the reference sensor, so as to transform thepositions to a substantially stationary frame of reference.

Preferably, bringing the position sensor to each of a plurality ofpoints comprises bringing the position sensor to a plurality of pointsin a patient's heart.

Preferably, the method includes measuring a physiological parameter atthe plurality of points, indicative of whether the point belongs to thearea to be measured.

Preferably, measuring the physiological parameter comprises measuring anelectrical activation signal at the plurality of points.

There is further provided in accordance with a preferred embodiment ofthe present invention, a method of aligning pieces of a fractured bone,comprising uniquely associating an anchor point with each of the pieces,determining for each piece coordinates of a plurality of points, whichare descriptive of the shape and position of the piece relative to theanchor point, moving the pieces so as to align the bone based on theshapes and positions of the pieces, repeatedly determining coordinatesof the anchor points while moving the pieces, and updating positioninformation regarding the pieces, based on the coordinates of the anchorpoints, for guidance in moving the pieces.

Preferably, determining the coordinates comprises transmitting andreceiving magnetic fields.

Preferably, uniquely associating an anchor point comprises fixing one ormore sensors to each of the pieces.

Preferably, updating the position information comprises calculating adistance between two pieces.

Preferably, the method includes notifying a user when the distancebetween two pieces is smaller than a predetermined distance.

Preferably, updating the position information comprises calculating thevolume of an area between two pieces.

Preferably, the method includes notifying a user when the volume issmaller than a predetermined value.

Preferably, the method includes producing an image of the pieces andupdating the image based on the updated position information.

Preferably, producing an image of the pieces comprises producing athree-dimensional image of the pieces.

Preferably, the method includes producing a model of a volume betweentwo pieces.

There is further provided in accordance with a preferred embodiment ofthe present invention, apparatus for intrabody measurement of an areawithin a body, comprising a probe for insertion into the area, aposition sensor mounted on the probe, a position determining system,which determines position coordinates of the sensor at a plurality ofpoints adjacent the area, and calculating circuitry, which calculatesdistances between the plurality of points.

Preferably, the position determining system determines the coordinatesby transmitting and receiving magnetic fields.

Preferably, the apparatus includes a screen for displaying a geometricalmap of the plurality of points based on the coordinates.

Preferably, the calculating circuitry calculates a volume of the area.

Preferably, the apparatus includes a modeling machine, coupled to thecalculating circuitry, which produces a model of the area responsivethereto.

Preferably, the circuitry calculates a density of the plurality ofpoints and signals a user as to areas in which the density is below apredetermined limit.

Preferably, the area is in motion, and the apparatus comprises areference catheter, including a reference sensor, wherein the positiondetermining system determines position coordinates of the referencesensor when determining the coordinates of the plurality of points, andthe calculating circuitry compares the coordinates of the plurality ofpoints to the coordinates of the reference sensor, so as to transformthe coordinates of the points to an inert frame of reference.

Preferably, the probe comprises a flexible catheter for insertion into apatient's heart.

Preferably, the catheter comprises an electrode for measuring electricalactivity at the plurality of points.

There is further provided in accordance with a preferred embodiment ofthe present invention, apparatus for aligning pieces of a fracturedbone, comprising a plurality of bone position sensors, which areconnected to corresponding pieces, a position determining system fordetermining positions of the sensors, a probe, including a probeposition sensor, which is passed over a plurality of points on thesurface of one or more of the pieces, wherein the position determiningsystem determines coordinates of the plurality of points, representativeof the shapes of the pieces, and calculating circuitry, which determinesand updates the coordinates of the plurality of points on the pieces,responsive to movements of the bone position sensors.

Preferably, the apparatus includes an imaging device for producing animage of the pieces, wherein the coordinates of the plurality of pointsare registered with the image.

There is further provided in accordance with a preferred embodiment ofthe present invention, apparatus for aligning pieces of a fracturedbone, comprising a plurality of position sensors, which are fixed tocorresponding ones of the pieces, an imaging device, which produces animage of the pieces, a position determining system, which determinesposition coordinates of the sensors, and calculating circuitry, whichassociates each piece seen in the image with its respective positionsensor and updates the positions of the pieces in the image, responsiveto changes in the coordinates of the sensors.

Preferably, the calculating circuitry automatically associates the imageof each piece with its respective position sensor according toattributes of the image of the piece.

Preferably, the calculating circuitry associates the image of each piecewith its respective position sensor according to information receivedfrom a user.

Preferably, the circuitry produces a geometrical map, based on thecoordinates, which is displayed along with the images of the fractures.

Preferably, the position determining system determines positions bytransmitting and receiving non-ionizing fields.

Preferably, the position determining system determines positions bytransmitting and receiving magnetic fields.

Preferably, the calculating circuitry calculates distances betweenpieces.

Alternatively or additionally, the calculating circuitry calculatesvolumes between the pieces.

Preferably, the apparatus includes a modeling machine, coupled to thecalculating circuitry, which produces a model of an area between thepieces responsive to the circuitry.

Preferably, the plurality of position sensors are mounted on screws,which are screwed into the pieces.

The present invention will be more fully understood from the followingdetailed description of the preferred embodiments thereof, takentogether with the drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a patient's heart with a measuringcatheter, in accordance with a preferred embodiment of the presentinvention;

FIG. 2 is a block diagram of measuring apparatus in accordance with apreferred embodiment of the present invention; and

FIG. 3 is a side cross sectional view of an arm with a fractured bonewhich is aligned in accordance with a preferred embodiment of thepresent invention; and

FIG. 4 is a schematic view of an arm with a fractured bone which isaligned in accordance with another preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a patient's heart 18 with a tricuspid valve 22 therein,which is measured in accordance with a preferred embodiment of thepresent invention. A measurement catheter 26 is situated within thepatient's heart near valve 22. A reference catheter 24, comprising aposition sensor 38, is situated at a fixed point relative to heart 18,preferably at the apex thereof, such that the movements of catheter 24coincide with the movements of heart 18.

Catheter 26 is preferably thin and durable and is suitable for insertioninto and maneuvering within the patient's heart. Such catheters aredescribed, for example, in PCT patent application U.S. Ser. No. 95/01103and in U.S. Pat. Nos. 5,404,297, 5,368,592, 5,431,168, 5,383,923, thedisclosures of which are incorporated herein by reference. Preferably,catheter 26 comprises a pressure sensor 36, at least one position sensor28, and one or more working channels 37 which allow attachment ofcatheter 26 by suction to points within heart 18. Such suction allowsconnection of catheter 26 to valve 22 in order to follow the movementsof the valve. Preferably, channels 37 are connected to a suction device(not shown), such as a pump, at the proximal end of the catheter.

FIG. 2 is a block diagram showing measuring apparatus 31 used to measureheart valve 22, in accordance with a preferred embodiment of the presentinvention. A position determining system 32 determines coordinates ofsensors 28 and 38, preferably by transmitting and/or receiving magneticwaves to or from the sensors, as described, for example, in PCTpublications PCT/GB93/01736, WO94/04938, and WO96/05768, in U.S. Pat.No. 5,391,199, or in PCT application PCT/IL97/00009, which is assignedto the assignee of the present application, all of which areincorporated herein by reference. Sensors 28 and 38 preferably compriseminiature coils.

Preferably, the coordinates determined by position determining system 32are stored in a memory 39 for further use. Calculating circuitry 30receives the determined coordinates and, based thereon, calculates thesize of intrabody regions. Circuitry 30 preferably is also connected toa display screen 34, on which images and/or geometrical maps ofintrabody regions may be displayed.

Pressure sensor 36 is preferably located adjacent the distal tip ofcatheter 26, as shown in FIG. 1. The relative blood flow at a pointwithin the heart may be determined according to the pressure measured atthe point, as is known in the art. Alternatively or additionally, a flowsensor at the tip of the catheter, for example, based on a Dopplerultrasound transducer, is used to directly measure the blood flow.

Preferably, an image of heart 18 along with catheter 26 is produced,before diagnosing the condition of valve 22. The image is preferably athree-dimensional image, produced using any suitable method known in theart, such as CT or MRI. Preferably, the image is displayed on screen 34and is associated with a geometrical map based on the determinedposition coordinates of the catheter. Preferably, during furtherprocedures, the geometrical map is continually updated, and circuitry 30updates the image on screen 34 accordingly.

Catheter 26 is used to diagnose the functionality of valve 22, in orderto allow a surgeon to decide whether valve 22 needs to be replaced. Thecondition of valve 22 is diagnosed by measuring the blood flow at pointsin the proximity of valve 22, in different states of the valve. Catheter26 is temporarily fixed to valve 22, preferably using suction throughchannel 37, or any other suitable method known in the art, and thendrifts freely according to the movements of the valve. Positiondetermining system 32 determines and, preferably, maps or plots thepattern of movement of valve 22. According to these movements, a surgeoncan observe whether valve 22 is in an open or closed state, and cantrack the motion of the valve.

Alternatively, a separate position sensor, preferably based on awireless transponder, as is known in the art, is attached to valve 22,thus allowing catheter 26 to be moved elsewhere, while the movements ofvalve 22 and of the separate sensor attached thereto are determined byposition determining system 32. The surgeon can thus correlate betweenthe state of valve 22 and the flow at points near valve 22, to determinewhether valve 22 is functioning properly. Alternatively, the surgeon candetermine the state of valve 22 solely according to the time pattern ofthe flow through valve 22.

The surgeon then decides according to the flow information whether toreplace valve 22. If valve 22 is to be replaced, it is preferablyimmediately measured, and a map of the valve is preferably produced inorder to prepare a replacement valve of proper size.

Preferably, catheter 26 is brought systematically to a plurality ofpoints in the proximity of valve 22, to produce a map of the valve. Theposition of each point is measured using position sensor 28, preferablyalong with a parameter characteristic of the adjacent tissue material,indicating whether the position belongs to heart muscle or to the valve,as described below. The position measurements are referred by circuitry30 to the position of reference catheter 24, in order to compensate forchanges in the position of catheter 26 due to the movements of heart 18.Preferably, the parameter characteristic of the tissue is determinedaccording to electrical activation signals received from the adjacenttissue, using an electrode 35. The heart's muscle tissue is generallycharacterized by electrical activation signals that pass through it,whereas the fibrous tissue of the valve has no electrical activation.Therefore, a map of valve 22 is determined by noting points which showlittle or no electrical activity.

Based on the map, circuitry 30 preferably calculates and reports thedimensions of valve 22. Preferably, circuitry 30 produces areconstructed three dimensional map of valve 22, which is displayed onscreen 34.

In a preferred embodiment of the present invention, the surgeon mayrequest that the map have at least a minimal density of determinedpoints. Circuitry 30 preferably notifies the surgeon of areas that donot have enough determined points, according to the surgeon'srequirement. In addition, the surgeon may decide independently, based onthe display on screen 34, to determine additional points in an area ofvalve 22. The surgeon accordingly moves the catheter tip through suchareas to determine additional points. The display on screen 34 isupdated to include the newly determined points.

In preferred embodiments of the present invention, circuitry 30 may beconnected to various types of ancillary apparatus, such as a modelcarving machine 33, which carves a model of valve 22 based on the map.The carved model can be used to choose and/or fabricate the new valve.

Preferably, the old valve is removed and the new valve is inserted bymeans of an endoscopic or other minimally invasive procedure. Theendoscope preferably includes position sensors so that the surgeon candirect the endoscope to points determined during the measuringprocedure. Thus, the new valve is inserted precisely to the points fromwhich the deteriorated valve was taken. Alternatively, a position sensoris connected to the valve to allow accurate positioning of the valvewithin the heart. After the insertion procedure, the operation of thenew valve is preferably checked in the same manner as the deterioratedvalve was checked.

FIG. 3 shows a fractured bone 43 which is aligned in accordance with apreferred embodiment of the present invention. A patient's arm 40 hasbeen opened in order to align pieces 42 of bone 43. Preferably, one ormore sensors 44, preferably comprising coils, as described above, arefixed to each of pieces 42. Sensors 44 serve as anchor points whichindicate the positions of their respective fracture piece.

In order to track the position of a piece it is sufficient to track theanchor point and update the positions of other points on the pieceaccording to their positions relative to the anchor point. Sensors 44are preferably screwed into pieces 42. Alternatively or additionally,sensors 44 are fixed to pieces 42 using a clamp, a staple, an adhesiveor any other suitable connection mechanism.

After sensors 44 are fixed to pieces 42, an X-ray or CT image of pieces42 is preferably produced and displayed on screen 34. Simultaneously,the positions of sensors 44 are preferably determined by a positiondetermining system 32. The position determining system is preferablycalibrated by circuitry 30 with respect to the image, as will now bedescribed.

In order for circuitry 30 to associate the determined positions ofsensors 44 with their respective images, the surgeon is preferablyprompted to point to each of sensors 44. Preferably, sensors 44 haveassociated fiducial marks 48, which appear clearly on the image and thussimplify identification of sensors 44 on the image. If a CT imagingsystem is used, fiducial marks 48 preferably comprise a radiopaquesubstance, such as aluminum. Alternatively, circuitry 30 automaticallyrecognizes sensors 44 according to their shape and/or their computeddensity.

In addition, the surgeon preferably associates each piece 42 with itsrespective one or more sensors 44 by pointing on the image to each ofpieces 42, along with its one or more respective sensors 44. Preferably,the outer surfaces or outlines of pieces 42 are also pointed out tocircuitry 30, to enhance the accuracy of the identification of pieces42. Alternatively or additionally, circuitry 30 may be programmed toautomatically recognize pieces 42 according to their shape and/or theircomputed density.

Alternative methods of associating between X-ray images and coordinatesof position sensors therein are described in U.S. Provisional PatentApplication No. 60/042,873, filed Mar. 31, 1997, which is assigned tothe assignee of the present invention and is incorporated herein byreference.

FIG. 4 shows another method for pointing out pieces 42, in accordancewith a preferred embodiment of the present invention. A probe 50, with aposition sensor 52 mounted on its tip, is passed over the surfaces ofpieces 42 through an incision in the skin of arm 40. Positiondetermining system 32 determines points on the surfaces of pieces 42,preferably at a high sampling rate, and thus the shape of pieces 42 isaccurately determined by circuitry 30. Preferably, circuitry 30 notifiesthe surgeon of areas on the surface of pieces 42 which do not have asampled point density above a predetermined value. The surgeonaccordingly will pass probe 50 over these areas in order to achieve therequired point density.

After calibration, the surgeon moves pieces 42 in an attempt to properlyalign bone 43. As pieces 42 are moved, the image on screen 34 ispreferably updated, based on position measurements by sensors 44, thusaiding the surgeon in aligning pieces 42. Preferably, more than one viewof pieces 42 is displayed on screen 34. Bone 43 may be aligned usingholding apparatus for keeping the fracture pieces fixed in place, asdescribed for example in U.S. Pat. No. 5,279,309 which is incorporatedherein by reference.

In a preferred embodiment of the present invention, circuitry 30continuously reports the distances between the pieces. In addition,circuitry 30 may continuously calculate the volume remaining betweeneach two adjacent pieces 42, based on the distance therebetween and thesurface areas of the pieces, determined in the measurement proceduredescribed above. Preferably, when the distance or volume are beneath apredetermined value, circuitry 30 signals the surgeon that the piecesare properly aligned.

In cases in which the surgeon observes that pieces of bone 43 aremissing, or otherwise cannot be perfectly aligned, circuitry 30 enableseasy fabrication of prosthesis. After the surgeon aligns pieces 42 aswell as possible, the surgeon actuates circuitry 30, to calculate thevolume and dimensions of empty areas between pieces 42. Alternatively oradditionally, maps of these areas are produced. Based on the calculatedvolumes, the surgeon decides whether artificial implants are to be usedto fill the empty areas. Preferably, a model of the area to be filled ora bone prosthesis is automatically produced by carving machine 33 orother machinery coupled to circuitry 30.

It will be appreciated that although the above embodiment has beendescribed with reference to aligning bone pieces following a fracture ofthe arm, the principles of the present invention may be used to measureand align any rigid fragments within a body, such as the vertebrae. Aposition sensor is preferably connected to each vertebra, and thedistance between the vertebrae is reported by the circuitry.

It will further be appreciated that although the above preferredembodiments are described as using magnetic field-based positiondetermining systems, the principles of the present invention may beapplied using any suitable position determining system known in the art,for example, an ultrasonic system.

It will be appreciated that the preferred embodiments described aboveare cited by way of example, and the full scope of the invention islimited only by the claims.

1. A method for assessing functionality of a valve in a heart, themethod comprising the steps of: providing a wireless transponder fortransmitting or receiving an ultrasound wave for determination ofposition coordinates of the wireless transponder; implanting thewireless transponder at a point on the valve; monitoring movements ofthe valve and the wireless transponder attached at the point on thevalve using a position determining system operated by using ultrasoundwaves for determining position coordinates of the wireless transponderby transmitting the ultrasound wave to the wireless transponder orreceiving the ultrasound wave from the wireless transponder; determiningposition coordinates of the wireless transponder using the positiondetermining system; and determining whether the valve is functioningproperly based on the position coordinates of the wireless transponder.